In order to fabricate a semiconductor device or a liquid crystal display (LCD) device, a process for forming a plurality of thin films is required. The thin film forming process is mainly performed by exposing technique, photolithography technique. Ultraviolet rays or X-rays are irradiated onto a substrate through a mask having a certain pattern thus to expose a photo-sensitive material deposited on the substrate, thereby forming the certain pattern on the substrate.
The exposing technique is utilized to pattern gate lines, data lines, and unit pixels of a liquid crystal display (LCD) device, and to form a color filter layer of a color filter substrate. Therefore, the exposing apparatus is very important in forming a precise pattern on the substrate.
Generally, the exposing apparatus is largely divided into a projection type for extraction/enlarge-transferring a mask pattern onto a substrate, and a proximity type for transferring a pattern onto a substrate by one to one using horizontal type parallel light.
The projection type exposing apparatus that can perform a contraction exposure is mainly used to fabricate a device requiring an integration such as a semiconductor device, and the proximity type exposing apparatus using a large mask is mainly used to fabricate an LCD device or a PDP having a large area on which same patterns are formed.
In the proximity type exposing apparatus, a mask has to be close to a substrate in order to completely transfer a mask pattern onto the substrate. In this case, the mask can come in contact with the substrate, which is called a contact type exposing apparatus. However, in case of the contact type exposing apparatus, foreign materials of the substrate may damage the mask. Therefore, it is a task to fabricate a mask stage proximate to a substrate without contact in the proximity type exposing apparatus.
The proximity type exposing apparatus and the projection type exposing apparatus respectively comprise a lighting device for generating light for exposure, a mask stage for supporting a mask having a certain pattern, a substrate chuck on which a substrate onto which the mask pattern is to be transferred is placed, and a supporter for supporting the substrate chuck.
The exposing apparatus is provided with a plurality of alignment cameras for certifying each position of the substrate and the mask stage in order to correctly align the substrate and the mask stage so as to precisely transfer the mask pattern onto the substrate. The alignment cameras correctly align the substrate and the mask stage by recognizing alignment keys formed on the substrate chuck or the substrate.
Accordingly as size of an LCD device is increasing recently, a mask stage for supporting a mask also becomes larger. A mask is fixed to a lower portion of the mask stage by a fixing means so that the mask can be proximate to a substrate.
The proximity type exposing apparatus will be explained with reference to FIG. 1.
Referring to FIG. 1, the proximity type exposing apparatus comprises a lighting device 101, a mask stage 105 formed at a lower portion of the lighting device 101 for supporting the mask 110, a supporter 120 for supporting four edges of the mask stage, a substrate chuck 130 formed at a lower portion of the mask stage 105 for supporting a substrate 114, a Y-axis driving stage 113 and an X-axis driving stage 112 for supporting and moving the substrate chuck 130, and a base stage 150 on which the X-axis driving stage 112 and the Y-axis driving stage 113 are formed.
The lighting device 101 generates light such as ultraviolet rays or X-rays thereby to transfer a mask pattern onto a substrate.
The mask stage 105 is composed of a lower stage 103 to which the mask 110 is directly coupled, and an upper stage 102 for supporting the lower stage and serving as a base of the mask stage.
In order for the mask 110 to be proximate to the substrate 114 as much as possible, the lower stage 103 to which the mask is directly coupled is coupled to a lower surface of the upper stage 102 thus to support the mask 110.
Each middle portion of the upper stage 102 and the lower stage 103 is empty so that light generated from the lighting device 101 can be irradiated onto the substrate 114 through the mask 110.
Four edges of the mask stage 105 are supported by the supporter 120 of a bar shape.
The substrate 114 supported by the substrate chuck 130, and the Y-axis driving stage 113 and the X-axis driving stage 112 for moving the substrate chuck 130 are installed below the mask stage 105.
The X-axis driving stage 112 can be installed on the base stage 150, or can be installed on a supporting chuck (not shown) formed on the base stage 150. A rail is installed on the base stage 150 or the supporting chuck in an X-axis direction, and the X-axis driving stage 112 is coupled onto the rail. A rail is installed on the X-axis driving stage 112 in a Y-axis direction, and a Y-axis driving stage 113 is coupled onto the rail.
The substrate chuck 130 is installed on the Y-axis driving stage 113, and the substrate 114 loaded onto the substrate chuck 130 is moved to a certain coordinate by the X-axis driving stage 112 and the Y-axis driving stage 113. Generally, a mask has a size larger than that of a substrate. Therefore, a plurality of exposures are performed by moving the substrate under a state that the mask is fixed, thereby transferring a mask pattern onto the entire substrate.
In the exposing apparatus for transferring minute mask patterns onto the substrate, the mask stage and the substrate have to be correctly aligned. Accordingly, an alignment camera (not shown) for a correct alignment between the substrate and the mask stage is provided on the mask stage. Also, an alignment key detected by the alignment camera is installed on the substrate or the X-axis driving stage.
The alignment camera certifies the alignment key thus to correctly align the substrate and the mask stage.
However, the conventional method for aligning the substrate and the mask stage has a problem. That is, since the substrate is moved by the X-axis driving stage 112 and the Y-axis driving stage 113 at the time of aligning the substrate and the mask stage, there is a limitation in aligning the substrate and the mask stage for a unit less than micro-meter.
Furthermore, since the substrate chuck is positioned on the X-axis driving stage and the Y-axis driving stage and the substrate to be exposed is placed on the substrate chuck, there is a limitation in obtaining a minute flatness of the substrate. In the proximity type exposing apparatus, a correct alignment of the substrate and the mask and a minute gap maintenance therebetween are very important.